In an operating alternating current machine, it is known that a magnetic flux exists in the region of the air gap. However, so far as now known, it has not previously been known that air gap flux (and, in particular, the peak amplitude of the fundamental component of this flux and its angular position in the air gap as the flux rotates) could be accurately measured on an instantaneous basis by using some other machine characteristic, such as the third harmonic component of the stator phase voltage.
No simple and reliable technique or apparatus was previously known which, when used in combination with an operating alternating current machine, would reliably and automatically determine the peak amplitude and relative position of the air gap flux using only a sensed third harmonic component of the stator phase voltage.
Such instantaneously existing information about the peak amplitude and location of the air gap flux, or an electric signal representative thereof, would be very useful in any one of a variety of applications, particularly in control devices and methods for regulating alternating current motor variables. Moreover, such control devices would themselves also be new and very useful, as would be the methods associated with their operation and use.
The art needs new and improved methods and apparatus for regulating the energy consumption of alternating current machines. The discovery of a reliable measuring technique for air gap flux makes possible a family of new and very useful devices and methods for regulating alternating current machine operation, performance and efficiency.